1. Field of the Disclosure
The present application relates to a display device adapted to enhance image quality.
2. Description of the Related Art
Recently, display devices have been developed to be thinner, lighter, and more portable, and to have a high performance. Flat panel display devices are receiving attention in the display field due to their reduced weight and volume compared to bulky cathode ray tubes (CRTs). The flat panel display devices include OLED (organic light-emitting display) devices which display images by controlling the amount of light emitted from an organic light emission layer.
The OLED devices are self-illuminating display devices employing a light emission layer between electrodes. As such, the OLED devices do not require a back light unit or the like contrary to liquid crystal display devices. Therefore, the OLED devices can be made thinner.
Such OLED devices display images using a plurality of pixels arranged in a matrix shape and each configured with 3 colored (i.e., red, green and blue) sub-pixels. Each sub-pixel includes an organic light emission cell and a cell driver independently driving the organic light emission cell.
The cell driver is configured with at least two thin film transistors and a storage capacitor which are connected between a gate line, a data line and a power supply line, in order to drive a pixel electrode of the organic light emission cell. The gate line is used to transfer a scan signal. The data line is used to transfer an image data signal. The power supply line is used to transfer a common voltage signal.
The organic light emission cell includes the pixel electrode connected to the cell driver, an organic layer disposed on the pixel electrode, and a cathode electrode disposed on the organic layer. As such, the OLED device includes an upper substrate and a lower substrate on which the thin film transistors and the organic light emission cells are formed.
The OLED device further includes a polarizing film. The polarizing film shields external light and enhances visibility of the OLED device. The polarizing film includes a poly-vinyl-alcohol (PVA) layer linearly polarizing light, a quarter wave plate (QWP) circularly polarizing light, and upper and lower tri-acetyl cellulose (TAC) layers disposed on upper and lower surfaces of the PVA layer.
Generally, a color shift phenomenon which forces a blue color to be visibly recognized is often observed in an OLED device. Such phenomenon is caused by retardation of the lower TAC layer and a spectral distribution property of the QWP. As a result, image quality of the OLED device is degraded.